Check out LibreHunt if you want something more hands-on. LibreHunt does a good job of explaining the merits of FLOSS and suggests Linux distributions based on how you answer its questionnaire.
First assess what you want and need in an OS. Do you want to maintain a similar workflow or do you want to learn a more minimal way of doing things?
Try Linux Mint, specifically the Cinnamon Edition. I believe in this OS enough that a USB flash drive with Linux Mint is always on my person in case someone wants me to set it up for them (perhaps I should have a utility belt with USB drives strapped to it; each drive would be flashed with a different OS).
Linux Mint provides a familiar interface and full-featured applications so the user can hit the ground running. The developers dedicate a lot of time to make the system intuitive without a sacrifice in customizability and I really appreciate that approach.
Take a look at OpenBSD. It follows the KISS philosophy, yet the system is robust enough to handle many different use cases (building a web server or a router is feasible using only the tools available in the base system).
OpenBSD feels transparent and comprehensible due to great documentation and minimal tools that work together. These things along with a proactive attitude toward security makes OpenBSD comfy, in a word.
That said, make no mistake: even though it comes with good defaults, OpenBSD requires a bit of reading. While full-featured desktop environments like GNOME are available, the system itself doesn't graphically abstract away tasks in the name of user-friendliness. Believe it or not, this is actually a blessing in disguise–if you learn how the system works as you go, that incremental understanding allows you to do new things and fix problems should they arise.
If you do install it, remember to consult the FAQ. It's particularly useful to newcomers as it shows you how to perform common tasks.
Use a privacy respecting OS for your mobile device if you can. GrapheneOS is what I use, although LineageOS supports a wider range of hardware.
Your router is a computer too. Proprietary consumer firmware isn't very capable, nor is it secure. DD-WRT, OpenWRT, pfSense, and OpenBSD are all much better options. If you decide to flash firmware onto a consumer router, use Ethernet and take the appropriate precautions.
Check out Building an OpenBSD router for more information on how I approach it.